Improved Off-Angle Solar Cells from Stanford

If it works the way I think it does, imagining it was the easy part. Building it was the hard part. The advent of 3D printers certainly created a lot more flexibility in how to fabricate it. But getting or making all the many different refractive indexes needed for this function, and laying down the layers smooth enough for good optical quality, seem like major feats.

Graded refractive indexes have long been used in optic fibers for data communications, to help gently guide spreading laser light back to the center to reduce dispersion and smearing of the data pulses, but I'm suspecting that the range of indexes needed to make this solar concentrator was vastly larger. It would be interesting to see a profile of index vs depth through the device, and to know what the maximum index is.

An additional advantage not pointed out in the article, is that most types of solar cells inherently have higher conversion efficiency with concentrated sunlight than with unconcentrated light.

I'm wondering if the Fresnel-like appearance is related to the use of multiple discreet layers. A theoretically ideal device would have a continuous gradient curve of refractive index, but these folks used closely stepped layers as an approximation, which can work quite well if the steps are small.